If you are in Florence, you won't need a car seat as everything is reachable by train/walking. When mine were that age (2 and 4 now) if I had to stay somewhere that didn't have a cot, I would try to put a mattress on the floor and they could sleep on that. Or at worst, put them on a bed and put pillows/blankets around on the floor in case of a fall.
Tell me exactly what you need and I will see what I can do. I live 40mins from Florence and can try and find a baby hire shop for you or maybe you could come over to me and borrow what you need! CAT me if you like